The invention relates generally to an anti-lock brake control system comprising at least two micro-computers which are fed the same rpm-signals, and which analyze these signals independently of one another, produce control signals from the rpm-signals, compare the control signals and produce a fault signal and/or a blocking signal upon any disagreement, or incongruence, between the control signals.
For apparatus which are particularly critical in safety matters, as is the case with anti-lock brake control systems, it is known and customary to provide a redundant structure, that is, to provide multiple parts pertinent to functional safety and to have them work in parallel so that the parts of the apparatus can "back up" one another with respect to the various functions.
Such a redundantly structured, self-controlling anti-lock brake control system is described in German patent document DE-PS 32 34 637.
In this apparatus, specially processed wheel-sensing signals are fed to two one-chip micro-computers arranged in parallel. From the sensed signals these micro-computers compute valve control signals and control signals. Each micro-computer is arranged with a comparator with both comparators being fed the control signals of both micro-computers as well as a computed valve driver signal of a respective micro-computer. Further, one comparator receives the control signal of the other micro-computer while the other comparator, after a gain adjustment, is fed a valve driver signal monitored at a magnetic valve. Upon a disagreement of valve control signals, that is, valve control signals and valve driver signals, or the control signals, a fault is detected. Each comparator can switch off the entire anti-lock brake control system or parts thereof via a governing stage and a relay.
This arrangement is unnecessarily cost-intensive, in particular due to the comparators. When these are included, either two unnecessary components are in the circuit which cost money and use space or, if each comparator is integrated into its micro-computer to form one module as suggested, high development expenses must be invested for this special module. At least a higher price must be paid for this module as compared to that for a micro-computer module.
In a further embodiment, logical circuit units (micro-computer and comparator) are each arranged with a monitoring and control circuit, which monitors and controls an impulse interval frequency of a corresponding switching circuit unit as well as a battery voltage of a vehicle. These monitoring and controlling circuits have proven to be relatively complicated and specialized modules in particular, because they must control the timing behavior of the anti-lock brake control system.
It is an object of this invention to provide a redundantly structured anti-lock brake control system which offers a maximum of safety while being constructed as uncomplicatedly and efficiently as possible and which, therefore, may be manufactured particularly cost-effectively.